Are you painting over the original paint?Perfectly fine to do if it is in good condition. There are 3 shades of gray Scotchbrite pads. The 7448, light gray is equivalent to 800-1000 grit, the 6448 dark gray is a slight bit more aggressive and the 7446 gray is equivalent to 120-150 grit.The 7447 Maroon is equivalent to 360 - 400 grit.

The idea with scuffing is to get the entire surface dull looking so the new paint has something to grab on to.